#include <iostream>
bool stack[10001];
char s[20001];

int main()
{
  for(int i = 0; i < 10; ++i)
  {
    int maxDepth = 0, maxCount = 0, count = 0, depth = 0, n;
    scanf("%d%s", &n, s);
    for(int j = 0; j < n; ++j) 
    {
      if(s[j] == '0' && depth > 0) 
      {
        if(depth > maxDepth)
          maxDepth = depth, maxCount = count;
        while(stack[depth] && --depth);
        stack[depth] = true;
        continue;
      }
      ++count;
      stack[++depth] = false;
    }
    printf("%d\n", maxCount);
  }
}